Vitamin D Alters Genes Involved in Follicular Development and Steroidogenesis in Human Cumulus Granulosa Cells

Abstract

Vitamin D deficiency is common among reproductive-aged women and has a role in female reproduction. This study evaluated the role of 1,25-dihydroxyvitamin D3 (vit D3) in ovarian follicular development and steroidogenesis by using a human granulosa cell (GC) model. Fifty-four women who underwent in vitro fertilization were enrolled. Follicular fluid (FF) and mural and cumulus GCs were collected from small and large follicles. In separate experiments, primary cumulus GCs were cultured with or without vit D3 followed by RT-PCR for mRNA expression levels. The effect of recombinant anti-Mullerian hormone (AMH) on nuclear localization of phospho-Smad 1/5/8 was evaluated in the presence or absence of vit D3 by using immunofluorescence. 25-Hydroxyvitamin D levels in FF as well as cell culture media AMH, progesterone, and estradiol (E2) concentrations were determined by ELISA and RIA. The following were measured: 1) mRNA expression levels; 2) 3β-hydroxysteroid dehydrogenase (3β-HSD) enzyme activity; 3) FSH-induced aromatase mRNA and E2 production; and 4) nuclear localization of phospho-Smad 1/5/8. In a multivariate analysis, 25 OH-D levels in FF negatively correlated with AMH and AMH receptor (AMHR)-II mRNA levels in cumulus GCs of small follicles. Compared with women with replete 25-hydroxyvitamin D levels in FF, those with insufficient/deficient levels had a 2-fold increase in AMHR-II mRNA levels in cumulus GCs of small follicles (P = .02). Treatment with vit D3 caused a decrease in AMHR-II and FSH receptor mRNA but an increase in 3-βHSD mRNA levels compared with control (P < .05). Vit D3 enhanced 3-βHSD enzyme activity as assessed by increasing progesterone release; however, vit D3 did not affect FSH-induced aromatase mRNA and E2 production, but it decreased the phosphorylation of Smad 1/5/8 and its nuclear localization. These data suggest that vit D3 alters AMH signaling and steroidogenesis in human cumulus GCs, possibly reflecting a state of GC luteinization potentiation.